1. Field of the Invention
The present invention relates in general to operation amplifiers (operational amplifiers). In particular, the present invention relates to an additional current source provided to accelerate the reference voltage output from the operation amplifier (operational amplifier) to a desired voltage.
2. Description of the Related Art
In a variety of systems of practical importance, a highly precise reference voltage source and operation speed is required. Conventionally, a standard reference voltage source is utilized to drive a relatively large capacitive load. FIG. 1 shows a conventional circuit diagram of an amplifier receiving a reference voltage to drive the large capacitive loading 14. The non-reverse input terminal of the operation amplifier (operational amplifier) 10 receives a reference voltage provided by a reference voltage generator 12, and outputs a voltage to drive the loading 14. The output voltage of the operation amplifier 10 is fed back to the reverse input terminal of the operation amplifier 10 and keeps increasing until reaching the reference voltage. However, the capacitance of the loading influences the time of the output voltage of the operation amplifier 10 reaching the reference voltage, that is, the larger the capacitance of the loading, the longer the time required for the output voltage to reach the target value. Moreover, the delay is more serious when starting up the circuit, which takes a lot of restoring time to charge the capacitive loading.
The object of the present invention is to provide a reference voltage providing circuit, which decreases restoring time after starting up and powering down.
To achieve the above-mentioned object, the reference voltage providing circuit includes an operation amplifier, a reference voltage generator, a current source, a switching device, and a pulse output device. The operation amplifier (operational amplifier) includes a non-reverse input terminal, a reverse input terminal and an output terminal coupled to the reverse input terminal for outputting an output voltage. The reference voltage generator is coupled to the non-reverse input terminal. The loading is coupled to the output terminal. The current source provides a starting current. The switching device is coupled between the current source and the output terminal, and turned on by an accelerating charging signal to pass the starting current to the loading through the output terminal. The pulse output device outputs the accelerating charging signal.